This invention relates generally to an antistaining coating formulation; a process for applying the formulation to a wood based substrate; and the resulting coated product which does not stain overlays that are attached to the coated product. Wood-based substrates which are suitable for this application include oriented strandboard, particleboard, plywood, fiberboard and solid-sawn lumber. Wood-based substrates which contain a significant concentration of extractable staining compounds are especially relevant to this invention. Overlays which could be used in conjunction with this invention include decorative coatings such as paints, and floor covering materials such as vinyl floor sheathing. Overlays that are placed in contact with wood based substrates are often stained by extractives from the wood, but the coated wood based substrates as treated according to the teachings of this invention are highly resistant to such staining.
Underlayment panels are installed on top of the structural subfloor and just beneath decorative floor coverings such as vinyl. The primary purpose of the underlayment is to act as a smooth, stable and uniformly thick substrate to which the decorative floor coverings are attached. The structural and other properties of oriented strandboard, particleboard and plywood, which are all currently used as underlayment panels, have generally been found to meet the underlayment application requirements, although all of these have stained vinyl floor coverings under adverse conditions of relatively high moisture content and high temperatures. After the wood-based underlayment is installed, a common product which is adhesively bonded or otherwise attached to the exposed strand surface layer is a vinyl floor covering. Many vinyl floor covering products are commercially available with one well known producer of a line of vinyl floor products being Armstrong World Industries, Inc. of Lancaster, Pa. Many suitable fill spread adhesives are commercially available materials commonly used to attach the vinyl floor covering to the wood surface. Other vinyl floor covering attachment means are perimeter adhesives and mechanical fasteners such as staples.
When vinyl floor covering is installed on top of oriented strandboard underlayment, there is a tendency for strand-shaped dark stains to develop on the upper surface of the vinyl 3-24 months after installation. Such staining is undesirable. Although the mechanism of stain formation is not clearly understood, there is a suspicion that over time under warm, humid conditions, water soluble compounds in the wood diffuse into the vinyl floor covering where some of them react with chemicals in the vinyl floor covering such as residual azodicarbonamide, which is a common blowing agent used in the manufacture of vinyl floor coverings. Some portion of the reaction products are probably intensely colored, and these manifest themselves as "stains." This staining action does not occur when azodicarbonamide is omitted from the vinyl floor sheathing formulation. Furthermore, certain vinyl floor covering products are more susceptible to staining than others. Thinner vinyl floor covering products develop these stains more readily than do thicker ones. The stains seem to develop most rapidly in hot, moist environments.
Other researchers have observed that this staining action can be prevented or "blocked" by placing a sheet of aluminum foil between the wood strand surface and the vinyl covering. Presumably the wood extractives are insoluble in the aluminum and thus are unable to migrate into the vinyl floor covering. Unfortunately, the aluminum is easily torn or punctured and the conventional adhesives used to secure the vinyl floor covering to the wood surface are not compatible with the aluminum. Other researchers have found that the aluminum fails to prevent staining when the surface of the aluminum is punctured or otherwise interrupted. Also, the aluminum foil is relatively expensive. Other total barrier coatings have similar problems and have proven to be less effective than aluminum foil at stain blocking.
It is also recognized that some commercially available patching compounds which contain high levels of Portland cement can be used as stain blocking coatings. Examples of such patching compounds include the MAPEI PLANI/PATCH roduced by MAPEI, INC., Montreal, PQ, Canada and Ardex Feather-Finish Cement roduced by Ardex, Inc. of Coraopolis, Pa. Although it is inconvenient to do so, these materials can be mixed with water or latex and trowelled onto the top surface of the underlayment at a residential house construction site. Installers must wait for the coating to set prior to installing the vinyl floor sheathing. This method is effective for preventing vinyl floor stains and it is practiced by some informed installers. We have discovered through experimentation that there is a minimum application load level that is required for effective stain blocking. At these loading levels the cost of the treatment is substantial. The short cure time of the cement makes these materials difficult to apply in a continuous process production line at a panel manufacturing site. Such an operation would require on-site mixing and sophisticated and complex process controls in order to avoid the risk of premature curing of the cement in the applicator equipment. On-site cleanup of cured cement is extremely difficult, time consuming and labor intensive.
The present discovery is that the staining action can be blocked very effectively over time without adversely affecting the vinyl adhesive bond by pretreating the top surface of the wood based surface with an aqueous suspension of an alkaline, inorganic, multivalent compound such as magnesium hydroxide. Included is a pigment to give the coating a preselected color and a binding agent to fix the stain blocking agent and pigment to the wood.
The preferred formulation has a shelf life of greater than 6 months which allows it to be manufactured off-site and then shipped to a panel manufacturing facility.
It is suspected that key wood extractives are precipitated or gelled or otherwise immobilized or made inert by the magnesium ions present in the preferred formulation. This coating has the advantages of being inexpensive, non-toxic, colored, stable with a long shelf life, compatible/receptive to vinyl adhesives and patching compounds and it will not fail if the coating is punctured. Formulations can be prepared which dry rapidly subsequent to application. We have found that as long as the spread rate of the coating is maintained below a certain threshold level, freshly coated panels can be stacked on top of each other with as little as 5 seconds of drying time under ambient conditions prior to stacking. Even when hundreds of these panels are stacked on top of each other with only minimum drying time, severe bonding between contacting, freshly coated panels is not observed. Selecting the proper binding agent and level of the binding agent are also critical to the success of avoiding bonding between stacked panels.
While it is possible to thoroughly dry the applied coating prior to stacking the coated panels, the use of a dryer, such as a forced-air oven, has many disadvantages relative to stacking the panels while they are still wet. High temperature dryers are expensive and they require relatively long sections of production line space. Dryers are also energy intensive. A dryer will heat at least a portion of the wood as well as the applied coating, and it is well known that heating wood generates volatile organic compounds (VOC's) which would need to be treated with some sort of pollution abatement equipment. We have also found that the top surface of a coated panel is more smooth when it is stacked wet than it is if it is dried prior to stacking.
The preferred manufacturing process for this coated underlayment entails coating the major faces of the flooring panels that will directly contact the vinyl floor coverings with the stain-blocker formulation; grading the coated panels; accumulating the coated panels for a period of about 30 seconds to 2 minutes; stacking the coated panels into units; packaging the units; and stacking units on top of units for storage.
One of the features desired by the building industry is for a product to arrive at a building site pretreated so on-site processes are minimized. The present invention includes application of the aqueous suspension of the preferred magnesium hydroxide and other additives at the manufacturing plant where it can be done on-line at relatively high speeds.
Upon arrival at a building site each pretreated panel will be ready for installation as a flooring underlayment panel. With the treated surface facing upwardly each panel will be fixed in place and thereafter the vinyl floor covering will be attached to the treated underlayment.
Accordingly, from the foregoing, the primary object of the present invention is the prevention of unwanted stains on overlays bonded to wood based substrates.
Another object is to provide a stain preventing application process that is performed prior to the point in time that the panels are shipped for sale into the distribution system.
Yet another object is to provide such a process that is a pretreatment coating process capable of being applied at high speeds.
Still a further object is to provide a stain prevention process and resulting product that is safe for the production workers and the environment.
Still a further object is to provide a pretreated wood-based panel product where the pretreating stain prevention compound will not adversely affect the overlay bonding mechanism over time.
Additionally, another object of the present invention is the provide a liquid stain blocking formulation that can be applied to any wood-based product, such as cedar lumber, and thereby prevents extractives in the cedar from migrating into top coats of paint which could be discolored by the staining compounds.
These and other objects of the invention will become more apparent upon reading the specification to follow.